Donald Trump has called for unity at California’s Republican Party convention as protesters demonstrated outside.

Mr Trump spoke to the convention for around 30 minutes ahead of the state’s primary on June 7, which could be crucial to him winning his party’s presidential nomination.

There are 172 delegate votes at stake in California and they could be vital to the billionaire businessman, who is chasing the target of 1,237 needed to clinch the nomination and avoid a contested convention.

The Republican front-runner told party members they needed to come together after their divisive primary but also delivered a warning.

He said: “There has to be unity in our party. Would I win – can I win – without it? I think so, to be honest with you, because they’re going to be voting for me (not the party).”

Mr Trump’s supporters bought tickets to the event and cheered for their candidate from a ring of tables around the perimeter of the ballroom. But his speech received a cooler reception from party veterans and donors who sat just beneath the stage.

Ohio governor John Kasich, who remains in the Republican race alongside Texas senator Ted Cruz, speaks to the convention on Friday evening. Mr Cruz and his new running mate, Carly Fiorina, address the convention on Saturday.

All three candidates are looking to galvanise supporters, sway undecided party members or poach from rival campaigns. The state party’s vice chairman, Harmeet Dhillon, said: “It’s going to be a free-for-all.”

Hundreds of demonstrators pushed to the front doors of the Hyatt Regency in Burlingame before being moved back by police in riot gear. Some protesters infiltrated the hotel building and hung a giant banner reading: “Stop Hate.”

The US Secret Service led Mr Trump in through a rear entrance to the hotel. He joked that he “felt like I was crossing the border”.

Mr Trump’s remaining rivals cannot beat him in what is left of the primary season. Their only hope is to deny him a majority of delegates heading into the July convention and fight for the prize in multiple ballots there.

But questions persist among Republicans – nationally and in California – about Mr Trump’s electability at the general election in November and his conservative credentials.

Mr Trump is viewed suspiciously by two camps in California – those who want to expand the party and those who view some of Mr Trump’s positions as betrayals of the conservative movement.

The convention crowd defies expectation in a state known as a Democratic fortress. There have been pushes toward moderation, but the group is strongly conservative and favours calls for free markets, tax cuts and shrinking the size of government.

It is also socially conservative. The state party’s platform defines marriage as between a man and a woman, and wants the US Supreme Court’s affirmation of abortion rights reversed.

Mr Trump has spoken favourably about Planned Parenthood, which provides abortion services. He has warned against cutting Medicare, Medicaid and Social Security, often targets for conservatives who want to slow government spending.

Mr Trump was a popular draw at a brief VIP reception, where he posed for pictures with party stalwarts. He later joked about having mud and dirt smeared all over him from his unorthodox entrance.

Henri Houdre was thrilled to see Mr Trump. “We see him as that alpha kid in high school with the leather jacket and slicked-back hair who everybody wants to be,” said the 18-year-old college student from San Francisco.

Mr Trump’s call to unity resonated with some. Kevin Krick, the Bay Area regional vice chairman for the Republican Party, said: “That’s the thing every Republican needs to keep in mind, that we’re the same team.”

Kersti Buchanan, 70, a retired translator and party activist from Mendocino County, who backs Mr Kasich, was shocked at all of Mr Trump’s supporters – and by his speech.

“He’s probably the most narcissistic person I’ve ever listened to,” she said. “It was fairly shocking to see this many people who are eating it all up.”

On Thursday night, protesters tangled with authorities and damaged police cars after a Trump rally in Orange County.

Protests that stayed mostly peaceful during the event grew in size and anger afterwards. Police in riot gear and on horseback pushed the crowd back and away from the Pacific Amphitheatre, where the rally was being held.

One of Mr Trump’s supporters had his face bloodied in a scuffle as he tried to drive away. One man jumped on a police car, leaving its front and rear windows smashed and the top dented, and other protesters sprayed graffiti on a police car and the venue’s marquee.

About 20 people were arrested, according to the Orange County Sheriff’s Department.